Guide apparatus

ABSTRACT

The present invention provides a down-hole tool guide apparatus  6  suitable for use in controlling movement of a down-hole apparatus  1  provided with a pressurised working fluid supply in a borehole P. The apparatus comprises: a body  7  having a chamber  13  in which is slidably mounted a piston  14.  A high pressure end  13   a  of the chamber  13  is connected  36  to the pressurised working fluid supply  10  for supplying pressurised working fluid to a high pressure side  32  of said piston  14.  A low pressure end  13   b  of the chamber  13  is connected with the outside of the guide apparatus  6  and is provided with a spring  16  for applying a biasing force to the low pressure side  17  of the piston  14  corresponding to a predetermined threshold pressure of the pressurised fluid supply at the high pressure side of the piston  14.  The body  7  mounts at least one shoe  25  having an engagement face  26.  The piston  14  is operatively coupled to a shoe displacement mechanism  18, 19, 28, 29  so that the shoe  25  is held in a stowed position when the piston  14  is urged towards the high pressure end  13   a  of the chamber  13  by the spring  16,  and is displaced outwardly so that the engagement face  26  projects outwardly of the body  7  when the piston  14  is displaced towards the low pressure end  13   b  of the chamber by supply of pressurised working fluid at a pressure higher than said threshold pressure.

[0001] The present invention relates to an active downhole cutting toolguide device for use in a hole with sides between which a hole-cuttingtool provided with said apparatus may be disposed.

[0002] There is a need for guiding of downhole cutting tools for variouspurposes including inter alia lateral or kick-off hole cutting,directional drilling, as well as to stabilise an existing cutting tooladvance direction against unwanted deviation therefrom. Existingsolutions to such problems are generally cumbersome to use and/orunsuitable for use with coiled tubing.

[0003] There is a need for cutting windows in oil/gas well casings usedto line the sides of well holes. Well casing is however normally verytough, thick walled steel pipe which is placed inside a borehole of awell as a lining to secure the borehole and prevent the walls thereoffrom collapsing. Casing—sometimes referred to as casing tubing—may beseamless, spiral welded or seam welded and may, for example, befabricated from various API grades of steel such as H40, J55, N80 orP110. Sizes typically vary from around 4 inches (101.6 mm) OD to 30inches (762 mm)OD, while weights typically range from around 11 lb/ft to200 lb/ft (16.4 kg/m to 298 kg/m approximately) depending on diameter,thickness and grade. It has also been known to employ glass fibrereinforced plastic casing.

[0004] It is known that the cutting of windows in oil well casing, asrequired for side tracking, is a complicated process, normally requiringthe use of a large number of tools not directly related to the cuttingof the window itself, such as whipstocks, packers etc. The normalprocedure is the setting of cement plug on top of a packer above which aso-called “whipstock” is placed. The whipstock basically consists of ahard metal wedge which guides a window milling drill bit gradually intothe casing thus cutting a slot in the casing. As the slope of thewhipstock is of a low value the pinching action on the drill bit is verysevere therefore requiring extremely high torque and yet a low rate ofprogress is achieved due to the high friction losses of the drill bitagainst the whipstock which have to be subtracted from the total energyavailable for the cutting of the window. Furthermore once the window hasbeen cut the whipstock and packer require to be retrieved which is oftena difficult and tedious process. To date the duration of an averagewindow milling job is three to four days and often much longer.

[0005] There is also a need for stabilising drilling tools used to clearwell holes which have become obstructed to a greater or lesser degree asa result of deposits on the sides thereof, and/or as a result ofdeformation of a well hole casing as a result of movement of thesurrounding strata. Conventional near bit stabilisers are essentiallypassive devices, typically comprising a heavy duty ring with fourangularly distributed wings which more or less closely approach the holesides thereby limiting the amount of deviation of the cutting toolpossible. With such stabilisers though the resistance to deviationremains substantially constant throughout use of the device i.e. duringtravel of the cutting tool along clear sections of the hole when ease oftravel is desired and stabilisation is not required, as well as duringcutting through obstructions, so that in practice the degree ofstabilization available when it is required is substantiallyinsufficient for proper stabilisation.

[0006] It is an object of the present invention to obviate or mitigateat least some of the aforementioned problems and disadvantages in theprior art.

[0007] It is a further object of the present invention to provide acutting tool guide apparatus which may be used with coiled tubing withits inherently shorter positioning and retrieval times against the useof jointed oil field tubing.

[0008] It is another object of the invention to provide a cutting toolguide apparatus suitable for down-hole use in a hole with sides betweenwhich a hole-cutting tool provided with said device may be disposed,whereby in use of the device at least one of the angle, the orientationand the lateral offset of a hole-cutting tool relative to thelongitudinal axis of the hole in which said tool is disposed, may becontrolled.

[0009] The present invention provides a down-hole tool guide apparatussuitable for use in controlling the path of the cutting tool of adown-hole cutting apparatus provided with a pressurised working fluidsupply in a borehole, said apparatus comprising: a body having a chamberin which is slidably mounted a piston, said body being formed andarranged for connection of a high pressure end of said chamber to thepressurized working fluid supply in use of the apparatus for supplyingpressurized working fluid to a high pressure side of said piston, saidbody being further formed and arranged for connecting a low pressure endof said chamber with the outside of said guide apparatus, said lowpressure end of said chamber being provided with a resilient biasingdevice formed and arranged for applying a biasing force to said pistoncorresponding to a predetermined threshold pressure of the pressurisedfluid supply at the high pressure side of said piston, so as to urgesaid piston towards the high pressure end of the chamber, said bodymounting at least one shoe, each said shoe having a radially outwardlyfacing longitudinally extending engagement face, said piston beingoperatively coupled to a shoe displacement mechanism formed and arrangedso that said shoe is held in a stowed position when said piston is urgedtowards the high pressure end of said chamber by the resilient biasingmeans, and said shoe is displaced outwardly so that said engagement faceprojects outwardly of the body when said piston is displaced towards thelow pressure end of the chamber by supply of pressurised working fluidat a pressure higher than said threshold pressure.

[0010] Thus with an apparatus of the present invention, it is possibleto apply a guiding force to a down-hole cutting tool as and whenrequired, simply by increasing the flow of working fluid. In general theguide apparatus of the present invention is intended for use with apressurised fluid operated cutting tool apparatus wherein is employed afluid operated motor such as a turbine or positive displacement motorand pressurised fluid is also supplied to the cutting tool forlubrication thereof, carrying away cuttings etc. Typically the guideapparatus would be mounted between the motor and the cutting tool, thelatter normally being supported on a thrust bearing unit. With such acutting tool apparatus the pressurised fluid pressure applied to thehigh pressure side of the cylinder(s) can be simply increased byincreasing the flow rate of the pressurised fluid supply delivered downthe drill string. The pressurised fluid supply is generally provided,downstream of the cylinder , with a flow restrictive nozzle in order toincrease the backpressure thereat and the pressure differential obtainedfor a given pressurized fluid flow rate. By suitable choice of thediameter of the flow restriction nozzle, it is possible to adjust thepressure differential obtained for a given flow rate. This has theadvantage of simultaneously increasing the motor torque and/or speed andthe fluid supply to the cutting tool which is exactly what is requiredwhen kicking-off or cutting through an asymmetric hole obstruction.Conversely when kicking-off or cutting through an obstruction, theguiding apparatus is automatically brought into operation by the workingfluid pressure increase which occurs with such operations.

[0011] In one form of the invention there may be used a single shoe. Inthis case displacement of the shoe into engagement with the holesidewall to one side of the drill string will force the cutting toolagainst the hole sidewall to the other side of the drill string. This isuseful in cutting windows in well casings by driving the cutting tool,conveniently a milling tool, laterally through the casing to cut awindow therethrough. The window may then be elongated longitudinally ofthe well by driving the drill string forwards. In this type ofarrangement, the angular directioning or orientation of the cutting tool(around the well) may be conveniently effected by means of a so-calledindexing means (which is a well known remotely operable device used toset the angular orientation of a tool on drill string) to control theangular orientation of the guide device and hence of the shoe around thewell prior to operation of the actuator means so that the cutting toolis forced against the well casing at a desired side of the well.

[0012] In another form of the invention at least two angularlydistributed, e.g. two diametrically opposed, or three, four or more,symmetrically distributed, shoes may be used. These may be displacedtogether by a single piston common thereto, or alternatively there maybe used two or more separate pistons for the various shoes. In this casewhen the cylinder(s) is (are) displaced, the existing drill stringdirection is stabilised against deviation, for example by asymmetricalobstruction to the cutting tool. This is particularly useful whenre-boring holes which have become obstructed to a greater or lesserdegree e.g. by the formation of deposits therein, or by deformation ofthe casing which could have arisen, for example, as a result of shiftsin the surrounding strata. Where it is merely desired to providestabilisation of an existing drill string direction, then control of theangular orientation of the guide apparatus with its shoes will notnormally be required. Nevertheless if desired the guide apparatus couldbe used in conjunction with an indexing device.

[0013] It will be appreciated that by varying the preloading of theresilient biasing means it is possible to adjust the fluid pressurethreshold required to activate the guide device by displacement of thepiston. Typically there could be used a threshold pressure in the regionof from 5 to 20 Bar, for example, about 10 Bar, when a positivedisplacement motor is used. Furthermore by choice of a suitable springrate, which may moreover be linear or non-linear, it is possible tomodify the rate of extension of the shoe(s) with increasing fluidpressure, for example, in order to control the force applied to thecutting tool.

[0014] Any convenient kind of shoe displacement mechanism may be used inaccordance with the present invention. Thus, for example, there could beused a cam mechanism, in which a cam is rotated to deploy the shoe(s).

[0015] Conveniently there is used a linkage mechanism captively securedto the piston and comprising a plurality of pivotally connected links.If used as a stabilizer form of guide apparatus of the invention, theshoes will be maintained parallel to the drill string. With the kick-offtool form of guide apparatus the shoe may lie at a slight angle to thedrill string as the tool is pushed over to one side of the tube and thetool bends.

[0016] The tool guide apparatus may be connected to the pressurisedworking fluid supply in any suitable manner. In general the tool guideapparatus will have a working fluid conduit extending axially throughits centre which can be coupled to the working fluid conduit(s) exitingthe motor stage and running through the thrust bearing assembly to thecutting tool. In such cases there is conveniently employed a perforatedconnector for coupling the working fluid conduit extending through theguide apparatus to that of the thrust bearing, for tapping off workingfluid pressure directly or indirectly into the high pressure end of theguide apparatus chamber. By varying the cross sectional area of theperforation(s), the amount of pressure drawn off in this way can besuitably adjusted.

[0017] Further preferred features and advantages of the invention willappear from the following detailed description given by way of exampleof some preferred embodiments illustrated with reference to theaccompanying drawings in which:

[0018]FIGS. 1 and 2 are general side elevations of a bottom holeassembly with a kick-off tool of the invention in its retracted anddeployed conditions;

[0019]FIGS. 3 and 4 are detailed sectional elevations of the kick-offtool;

[0020]FIG. 5 is a detail front elevation of the kick-off tool in itsretracted condition;

[0021]FIG. 6 is a transverse section of the kick-off tool in the planeVI-VI in FIG.4;

[0022]FIG. 7 is a sectional elevation of a centralizing tool of theinvention;

[0023]FIGS. 8 and 9 are schematic transverse sections through thecentralizing tool of FIG. 7 in its deployed and retracted condition; and

[0024]FIG. 10 is a longitudinal section of a cutting tool suitable foruse with a kick-off tool according to FIGS. 3 to 6 for window milling.

[0025]FIGS. 1 and 2 show (schematically) a bottom hole assembly 1suspended from a coiled tubing drill string 2 and comprising a downholemotor 3 and drill bit 4 supported on a thrust bearing unit 5 with akick-off tool 6 of the invention mounted between the thrust bearing 5and the motor 3. In FIG. 1 the kick-off tool 6 is in its inactive orstowed condition, whilst in FIG. 2 the kick-off tool is shown fullyextended.

[0026] As shown in FIGS. 3 and 4 the kick-off tool 6 comprises agenerally tubular body 7 having a reduced internal diameter upperportion 8 and a larger internal diameter lower portion 9. A fluid supplytube 10 extends along the central longitudinal axis X-X of the body 7closely fitting the interior 11 of the upper body portion 8 and spacedfrom the interior 12 of the lower body portion 9 so as to define anannular chamber 13 therebetween. An annular piston 14 is slidablymounted between the fluid supply tube 10 and the interior 12 of thelower body portion 9. A central intermediate diameter body portion 15houses a helical spring 16 which engages the upper end 17 of the piston14 for resiliently biasing the piston 14 downwardly.

[0027] The upper end 17 of the piston 14 has secured thereto a connector18 which is pivotally connected 19 to the lower end 20 of a shoeassembly 21, the upper end 22 of which is pivotally connected 23 to part24 of the upper body portion 8. In more detail the shoe assembly 21comprises an elongate shoe member 25 having an outer engagement surface26 with closely spaced longitudinally extending ridges 27 for positiveengagement in use of the tool with the side of a hole or pipe andstabilizing the tool against angular displacement whilst permittinglongitudinal displacement—for example, for window milling (longitudinalhole elongation). The ends 25 a, 25 b of the shoe member 25 areconnected by respective link members 28, 29 to the piston 14 and upperbody portion 8, so that the shoe assembly 21 is movable between a stowedradially retracted configuration as shown in FIG. 3 with the shoe member25 and link members 28, 29 fully extended longitudinally, and a deployedradially extended configuration as shown in FIG. 4 with the shoe member25 and link members 28, 29 partially collapsed together longitudinally.

[0028] The working end portion 30 of the piston 14 has a reduceddiameter and is slidably received within a sleeve 31 mounted within theannular chamber 13 in order to reduce the surface area of the workingend face 32 of the piston 14 thereby to reduce the force exerted on theshoe assembly 21 for a given differential fluid pressure exertedthereon.

[0029] The lower end 33 of the fluid supply tube 10 is connected via atubular coupling 34 (see FIG. 4) to a further fluid supply tube section35 extending through a thrust bearing unit 5. The tubular coupling 34has a number of apertures 36 which connect the interior 37 of the fluidsupply tube 10 to the high pressure end 13 a of the annular chamber 13below the piston working end face 32 for supplying fluid pressurethereto. Inside the coupling 34 is provided a flow restriction nozzle 38for increasing the fluid pressure diverted to the chamber 13. Theback-pressure generated and the pressure differential obtained for agiven flow rate can be adjusted by selecting a suitable flow restrictionnozzle diameter. The low pressure end 13 b of the annular chamber 13above the piston 14 is open to the outside of the guide apparatus 6around the shoe member 25 (see FIGS. 3 to 6).

[0030] In use of the kick-off tool of FIGS. 3 to 6, under normaloperating conditions, the shoe member 25 is held in its retractedposition by the spring 16. When the differential fluid supply pressureexerted on the working end face 32 is increased by increasing the flowrate of the pressurized fluid, then the piston 14 is forced upwardlythereby partly collapsing the shoe assembly 21 and forcing out the shoemember 25 into a radially outwardly deployed position in engagement withone side 40 of the hole or pipe 41 inside which the bottom hole assembly1 is disposed and forcing the latter towards the other side 42 of thehole or pipe 41 in order to, for example, bring a window cutting tool(not shown) into engagement therewith, deviate the drilling directionetc.

[0031] FIGS. 7 to 9 show a centralizing tool 43 of the invention for usein centralizing a bottom hole assembly 1 and stabilizing it againstunwanted deviations e.g. due to asymmetric obstructions in the hole orpipe 41 or other asymmetric resistance to the advance of the bottom holeassembly 1. The centralizing tool 43 is of essentially similarconstruction to the kick-off tool 6 of FIGS. 1 to 6 but with threesymmetrically angularly distributed shoe assemblies 21A, 21B, 21Cinstead of the one shoe assembly 21 of the kick-off tool 6, and similarcomponents corresponding generally to those of the latter are indicatedby like reference numbers. In this case when the differential fluidsupply pressure applied to the piston working end face 32 is increasedthe shoe members 25 are brought into engagement with the sides 45 of thehole or pipe 41 around the tool 43 so that the bottom hole assembly 1 isheld firmly in the centre of the hole or pipe 41 against unwanteddeviations therefrom.

[0032] As may be seen in Fig.6, the side 46 of the kick-off tool 6 has asubstantially larger radius of curvature (comparable to that of the toolwith the shoe assembly 21 in its deployed, radially extended position)than that of the tool 6 in its radially retracted condition. By thismeans the surface area of the tool side 46 which is forced intoengagement with the pipe side 42 in which, for example, a hole is to becut, is maximized thereby spreading the load thereon, whilst at the sametime maximizing ease of movement of the tool 6 along the pipe 41 whenthe shoe assembly 21 is in its radially retracted condition.

[0033]FIG. 10 is a longitudinal section of a cutting tool suitable foruse with a kick-off tool according to FIGS. 3 to 6 for window milling.In more detail the cutting tool 47 has an outer generally cylindricalcutting surface 48 which may have carbide inserts or crushed carbideparticles or similar cutting materials brazed or attached on to it. Thiscylindrical cutting surface 48 will cut during the initial perforatingoperation as the kick-off tool 6 is actuated and pushes laterally themilling tool 47 into the wall of the tubing P (see FIGS. 1-2). The frontend face 49 of the tool has a central recess 50 made of a generallyconical form. This end face 49 will also be coated with an abrasivecutting coating e.g. crushed carbide. Once the perforation has been madeand the BHA starts to advance down the well to elongate axially theperforation to form a window in the tubing P, the end face 49 will bethe cutting face. The conical recess 50 of the end face 49 is designedto stabilise the BHA so that it does not drift back into the centre ofthe tube P, by tending to centralise the cutting 47 in the wall of thetubing P. (If a flat face or an external conical face is used, the tooltends to push back in towards the centre of the tubing).

[0034] It will be appreciated that various modifications may be made tothe above described embodiment without departing from the scope of thepresent invention. Thus, for example, although in FIGS. 3, 4 and 7, thepiston-cylinder device 14, 13 is shown connected to the lower end of theshoe assembly, the piston-cylinder device could also be connected to theupper end thereof. It is believed that in use a piston located connectedat the lower end could be advantageous as if the tool becomes difficultto operate, e.g. because of contaminants in the pressurized fluidcausing a blockage, then in the process of withdrawing the tool from thehole the piston is pushed back by the force of the springs and the leveraction of the shoe without having to overcome the effect of the blockageor debris above the piston. To encourage the shoe to retract on pull outof the hole, the angle of the links 28 and 29 at full extension shouldbe less than 90° from centreline of the body and preferably in the rangefrom 30 to 60°.

[0035] Also, if it is desired to provide axial stabilization againstlongitudinal displacement of the tool—for example in use as aperforating tool, where a hole is to be made in the wall of thecasing/tubing but a window is not required, or in use as an anchor,then, instead of longitudinally extending grooves and ridges 27, therecould be used part-annular grooves and ridges. In use as an anchor theguide apparatus would be positioned between the downhole motor 3 and thecoiled tubing/drill string 2. As a stabiliser the guide apparatus may bepositioned between the downhole motor 3 and the coiled tubing/drillstring 2 or between the downhole motor 3 and the bearing section 5.

[0036] To reduce the possible bending of the bottom hole assembly 1between the drill bit 4 and the guide apparatus 6 it may be advantageousto integrate the bearing section 5 and the guide apparatus 6 into asingle unit.

What is claimed is:
 1. A down-hole tool guide apparatus suitable for usein controlling movement of a down-hole apparatus provided with apressurised working fluid supply in a borehole, said apparatuscomprising: a body having a chamber in which is slidably mounted apiston, said body being formed and arranged for connection of a highpressure end of said chamber to the pressurized working fluid supply inuse of the apparatus for supplying pressurized working fluid to a highpressure side of said piston, said body being further formed andarranged for connecting a low pressure end of said chamber with theoutside of said guide apparatus, said body being provided with aresilient biasing device formed and arranged for applying a biasingforce to said piston corresponding to a predetermined threshold pressureof the pressurised fluid supply at the high pressure side of saidpiston, so as to urge said piston towards the high pressure end of thechamber, said body mounting at least one shoe, each said shoe having aradially outwardly facing longitudinally extending engagement face, saidpiston being operatively coupled to a shoe displacement mechanism formedand arranged so that said shoe is held in a stowed position when saidpiston is urged towards the high pressure end of said chamber by theresilient biasing means, and said shoe is displaced outwardly so thatsaid engagement face projects outwardly of the body when said piston isdisplaced towards the low pressure end of the chamber by supply ofpressurised working fluid at a pressure higher than said thresholdpressure.
 2. An apparatus as claimed in claim 1 wherein is provided asingle said shoe, whereby said apparatus may be used as a kick-off tool.3. An apparatus as claimed in claim 1 wherein is provided a plurality ofangularly distributed said shoes, whereby said apparatus may be used asa centralising or anchoring tool.
 4. An apparatus as claimed in claim 3wherein said shoe engagement faces are provided with longitudinallyextending ridges, whereby said apparatus may be used as a centralisingtool.
 5. An apparatus as claimed in claim 3 wherein said shoe engagementfaces are provided with part annularly extending ridges, whereby saidapparatus may be used as an anchoring tool.
 6. An apparatus as claimedin claim 3 wherein is provided a single said piston and chamberoperatively coupled to a shoe displacement mechanism for each of saidshoes.
 7. An apparatus as claimed in claim 1 wherein said shoedisplacement mechanism comprises a camming device formed and arrangedfor acting between the piston and shoe(s) so as to provide a progressiveradially outward displacement of said shoe(s) in response to an axialdisplacement of the piston.
 8. An apparatus as claimed in claim 1wherein said shoe displacement mechanism comprises a linkage havingspaced apart portions pivotally connected to respective ones of theshoe(s) and the piston, said shoe(s) being captively mounted to saidbody so that a progressive radially outward displacement of said shoe(s)is provided in response to an axial displacement of the piston.
 9. Anapparatus as claimed in claim 1 wherein said chamber and piston areannular.
 10. An apparatus as claimed in claim 9 wherein a conduit forsaid pressurised working fluid supply extends through said chamber alonga central longitudinal axis thereof.
 11. An apparatus as claimed inclaim 1 wherein said resilient biasing device comprises a helicalspring.
 12. An apparatus as claimed in claim 1 wherein said resilientbiasing device has a predetermined preloaded so as to require apressurised fluid threshold pressure for initiating piston displacement,in the range from 5 to 20 bar.
 13. An apparatus as claimed in claim 1wherein said resilient biasing device has a variable spring rate.
 14. Anapparatus as claimed in claim 1, wherein said chamber is connected tothe interior of a pressurised fluid supply conduit, via at least oneperforation in said conduit.
 15. An apparatus as claimed in claim 1wherein the pressurised fluid supply is provided, downstream of itsconnection to the high pressure end of said chamber, with a flowrestrictive nozzle in order to increase the backpressure thereat and thepressure differential obtained for a given pressurised fluid flow rate.16. A pressurised fluid operated downhole cutting tool apparatus havinga pressurised fluid—operated motor drivingly connected to a cutting tooland a pressurised fluid supply, wherein is provided a guide apparatusaccording to claim
 2. 17. An apparatus as claimed in claim 16 whereinsaid guide apparatus is mounted between the motor and the cutting tool.18. An apparatus as claimed in claim 16 wherein said motor is selectedfrom a positive displacement motor and a turbine.
 19. A pressurisedfluid operated downhole apparatus provided with an anchoring toolcomprising a guide apparatus according to claim 3.